Method and system for providing visual and electrical read-out in signal-to-image storage tube



June 18, 1968 w. w. GREUTMAN 3,389,293

METHOD AND SYSTEM FOR PROVIDING VISUAL AND ELECTRICAL READ-OUT IN SIGNAL-TOIMAGE STORAGE TUBE Filed Nov. 6, 1964 2 Sheets-Sheet 1 Z4 47 n'u G h is Z1 13 as I J a Q i 47 t w' Q 5!! k 'II 54 a ea. 7 Q 5i! 5.9 58 is /3 W050 E! June 18. 1968 w. w. GREUTMAN 3,389,293

METHOD AND SYSTEM FOR PROVIDING VISUAL AND ELECTRICAL READ-OUT IN SIGNAL-TO-IMAGE STORAGE TUBE Filed Nov. 6, 1964 2 Sheets-Sheet 2 g pe-fame 6) 63 Fig.5 27 g 5/ 7a Z2 Z0 w u n 6" 0 1'4" )7 by MWMZM United States Patent 3,389,293 METHOE AND SYSTEM FOR PRGVIDING VISUAL AND ELECTRICAL READ-OUT IN SIGNAL-T0- IMAGE STQRAGE TUBE Weldon W. Greutman, Hiclrsvilie, Ohio, assignor to international Telephone and Telegraph Corporation, a corporation of Delaware Filed Nov. 6, 1964, Ser. No. 409,382 7 Claims. (Cl. 315-12) ABSTRACT OF THE DESCLOSURE An image storage tube selectively provides visual and electrical read-out. A writing beam stores a charge image on an insulator screen which then modulates a hood beam to display the image on a display screen. Electric read-out of the image is provided by a Writing beam of increased current which is on simultaneously with the flood beam. Output signal is taken from the backing electrode of the insulator screen or a collector electrode.

This invention relates generally to signal-to-image charge storage tubes and to methods and systems for operating such tubes, and more particularly to a method and system for selectively providing both visual and electrical read-out with a conventional signal-todmage charge storage tube.

Signalto-image charge storage tubes are commonly employed in radar and other information transmission systerns for storing video signal information as it is received and thereafter visually displaying such information. Another form of storage tube is the signal-to-signal tube, the barrier grid storage tube being a typical example, such tubes again storing video signal information as it is received, the information thereafter being read-out in elec trical signal form.

here are applications in which it is desirable to provide either visual or electrical read-out of stored video signal information. For example, it may be desirable to store video signal information as it is received, to then view the stored information and if it is found to be satisfactory thereafter to read-out the stored information in electrical signal form. In the past, such applications have required the employment of both a signal-to-image or direct viewing storage tube, and a signai-tosignal storage tube. It is therefore desirable to provide a method and system in which both visual and electrical readout may be obtained with the same storage tube. A storage tube and system providing both visual and electrical read-out is described and illustrated in Patent No. 3,089,055, to N. H. Lehrer. However, the tube disclosed in that patent is not a conventional direct viewing storage tube, but is rather a special tube and thus the method and system described is not applicable to existing conventional direct viewing storage tubes. it is therefore farther desirable to provide a method and system for obtaining both visual and electrical readout with a conventional type of direct viewing storage tube.

in accordance with the broader aspects of the invention, a conventional direct viewing storage tube is employed of the type having a phosphor display screen, a charge storage screen comprising an insulator screen and a metal backing screen, writing electron beam gun with means for scanning the writing beam over the insulator screen, a flood electron beam gun, and a collector electrode. In accordance with the invention, with the tube in normal operating condition, the storage screen is erased to the cut-off condition and the desired information is then writ-ten into storage in the normal manner and may be viewed if desired in the normal manner. In order to provide the electrical read-out, the Writing beam with the beam current increased to saturation level, is scanned over the insulator screen with the flood beam on, and the resulting current flow in either the metal backing screen or the collector electrode is detected.

It is accordingly an object of the invention to provide an improved method for obtaining both visual and electrical read-out with a conventional signal-to-image charge storage tube.

Another object of the invention is to provide an improved system for obtaining both visual and electrical read-out with a conventional signal-to-im-age charge storage tube.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram showing one embodiment of the system of the invention;

FIG. 2 is a schematic diagram showing another embodiment of the system of the invention; and

FIG. 3 is a fragmentary schematic diagram useful in explaining the method of the invention.

Referring now to FIG. 1, there is shown a conventional signal-to-image or direct viewing storage tube, generally identified at It}, having an evacuated enclosing envelope 11 with a faceplate 12 at one end thereof and with neck portions 13, 14 at the other end thereof. A conventional phosphor display screen 15 is deposited on the inner surface of faceplate i2 and conventional flood and writing electron beam guns 16, 17 are respectively positioned in neck portions 13, 14 of envelope 11. Flood gun 16 includes a conventional cathode 18 and a conventional anode 19 while writing beam gun 17 includes a conventional cathode 20, control grid 22, anode 23 and horizontal and vertical writing beam deflection elements 24, 25.

A conventional perforate charge storage electrode 26 is positioned in envelope 1]. and comprises an insulator screen 27 and a metal backing screen 28. A conventional collector electrode 29 is positioned in envelope 11 spaced from insulator screen 27 and conventional flood beam collimating conductive wall coatings 3t), 32 and 33 are provided as is well known to those skilled in the art.

Phosphor display screen 15 is connected to terminal 34 which in turn is connected to a suitable source of potential, such as +8000 volts in a specific embodiment. Backing screen 28 is connected to switch 35 having first and second positions 36, 37 respectively connecting the backing screen 28 to terminals 38, 39. Terminals 38, 39 are in turn respectively connected to suitable sources of writing and erasing potential, such as +5 volts and +10 volts in the specific embodiment. Collector electrode 29 is connected to terminal 40 which in turn is connected to a suitable source of collector potential, such as volts in the specific embodiment, collector screen 29 thereby collecting secondary electrons which are emitted from the surface of insulator screen 27 due to impingement of the writing electron beam thereon. Wall coatings 39, 32, 33 are respectively connected to terminals 42, 43, 44 which, in turn, are respectively connected to suitable sources of 3 potential, such as +120 volts, volts and +50 volts in the specific embodiment.

Anode 19 of flood gun 16 is connected by switch to terminal 46 which in turn is connected to a suitable source of anode potential, such as volts in the specific embodiment. Cathode 18 of flood gun 16 is connected to ground 47 in the specific embodiment, as shown.

Cathode 20 of writing gun 17 is connected to terminal 47 which in turn is connected to a suitable source of potential, such as +600 volts in the specific embodi ment. Anode 23 is connected by switch 48 to terminal 49, which in turn is connected to a suitable source of anode potential, such as +25 volts. Vertical and horizontal deflection elements 24, 25 are respectively connected to terminals 50, 52 which in turn are coupled to conventional vertical and horizontal sweep generators, as is well known to those skilled in the art.

In accordance with the invention, a switch 53 is provided having elements 54, 55 and first and second positions 56, 57. Element 54 of switch 53 in its first position 56 connects control grid 22 of writing gun 17 to coupling capacitor 53 which in turn is connected to video signal input terminal 59 which is adapted to be connected to a source of video signals to be stored (not shown). Switch element 55 in its first position 56 connects bias voltage terminal 60 to bias resistor 62 which in turn is connected to control grid 22 of writing gun 17, terminal 60 in turn being connected to a suitable source of normal bias voltage, such as 650 volts in the specific embodiment, thereby to provide normal writing beam current for normal writing operation of the tube. Switch element 55 in its second position 57 connects bias voltage terminal 63 to bias resistor 62, terminal 63 being connected to a second source of suitable bias voltage,

such as +610 volts in the specific embodiment, to therei by provide increased writing beam current for electrical read-out operation, as hereinafter described. In the illustrated embodiment, a suitable load resistor 64 is serially connected between terminal 38 and switch 35 and electrical read-out output terminal 65 is coupled to the midpoint between resistor 64 and switch 35 by coupling capacitor 66.

Referring now additionally to FIG. 3, an incremental segment of the storage screen 26 is shown including one of the apertures 67 extending through the insulator screen 27 and metal backing screen 28. Assuming now that a charge pattern or image has previously been stored on the insulator screen 27 by secondary emission of electrons therefrom due to scanning of the normal beam current writing beam 68 thereover, the writing beam being intensity modulated by control grid 22, in accordance with the input video signal information, as is well known to those skilled in the art, switch 35 is then moved to position 37 to apply +10 volts potential to the backing screen 28. Switch 48 is then opened to turn off the writing beam 68 and switch 45 is closed to turn on the flood beam 69; flood beam 69 is a low velocity beam of electrons which completely floods the entire surface area of the insulator screen 27, as is well known to those skilled in the art. Under this condition, and with the flood cathode 18 connected to ground, as shown, the electrons of the flood beam 69 will charge the surface of insulator screen 27 to essentially the potential of the flood cathode 18, i.e., ground in the specific embodiment, and thus it will be seen that a 10 volt charge exists between the metal backing plate 28 and the front surface of the insulator screen 27. The stored image is thus erased to cut-off and switch 35 is then returned to its position 36 to connect backing screen 28 to the +5 volt source of potential. Recalling that 10 volt charge was provided on the insulator screen 27 with reference to the backing screen 28 as a result of the crasing action of the flood beam 69, reduction of the potential of the backing screen 28 to +5 volts will reduce the potential of the front surface of insulator screen 27 to +5 volts immediately after erasure, i.e., the same potential differential will exist between the backing screen 28 and the front surface of the insualtor screen 27.

With switch 35 remaining in its position 36 thereby applying the +5 volt potential to the backing screen 23, with switch S3 in its position 56 thus coupling the video signals and the 650 volt bias potential to the control grid 22 of writing gun 17, switch 48 is closed and the writing beam 68, intensity modulated by the video signals, is scanned by deflection elements 24, 25 over the insulator screen 27, the intensity of the beam 68 thus varying in response to the modulation by the input video signals up to a maximum beam current established by the +650 volt bias potential connected to terminal 60. This scanning of the front surface of the insulator screen 27 by the high velocity modulated writing beam, will, by secondary emission from the insulator screen 27, provide a charge pattern or image on the insulator screen 27 varying from +5 volts to zero potential in accordance with the modulation of the writing beam 68; maximum beam current corresponding to a white video signal will bring the surface of insulator screen 27 up to zero volts Whereas minimum beam current corresponding to black video signal information will leave the potential of the surface of insulator screen 27 essentially the +5 volt level established during erasure.

In order to view the charge image thus written onto the surface of insulator screen 27, switch 45 is closed thereby initiating the flood beam 69. In those incremental areas of the insulator screen 27 which remain at the +5 volt level, i.e., black, the electrons of the flood beam 69 will be repelled to the collector electrode 29 so that none of them pass through the respective aperture 67 to the display screen 15, thus resulting in a black picture element. On the other hand, in those incremental areas of the surface of insulator screen 27 which have been brought up to zero potential by the writing beam 68, the electrons of the flood beam 69 will pass through the respective apertures 67 to the display screen 15 thus providing a white picture element. It is thus seen that the electrons of the flood beam 69 pass through the apertures 67 in the storage electrode 26, being modulated by the charge image previously written onto the insulator screen 27 by secondary emission due to impingement of the scanned writing beam 68 thereon, thus providing a displayed image corresponding to the charge image, and in turn to the input video signal. it will be readily understood that the operation of the direct viewing storage tube 10 as above described during erasure, writing and viewing, is conventional and does not form a part of the present invention.

In order to provide electrical read-out of the charge image previously written onto the storage screen 27, as abovedescribed, switch 35 is maintained in its position 36 coupling the +5 volt source of writing potential to the backing screen 28, switch 45 is maintained closed thus leaving the flood beam 69 turned on, however, switch 53 is moved to its second position 57 thereby disconnecting the source of video signals from the control grid 22 of the writing gun 17 and connecting the +610 volt bias voltage source thereto, thereby to provide a fixed writing beam current higher than the maximum provided during the normal writing operation. With switch 48 maintained closed, the writing beam 68 having increased beam current is then scanned over the storage screen 27 which is simultaneously being flooded with the flood beam 69 from the Hood gun 16. The secondary emission from the surface of insulator screen 27 due to impingement of the higher intensity writing beam 68 thereon tends to charge the surface of the insulator screen positive with respect to ground. However, the flood electrons provided by the flood beam 69 maintain essentially zero equilibrium potential on the surface of the insulator screen, with a resultant current flowing, by capacitor action, in the metal backing screen 28 and load resistor 64, this current varying in accordance with the initial charge on the insulator screen previously written by the writing beam during its normal writing operation. Thus, an electrical output signal is provided across the load resistor 64 and at the output terminal 65. It is important to observe that in order for the flood electrons of the flood beam 69 to maintain the zero equilibrium potential on the surface of the insulator screen 27 during scanning by the higher current Writing beam 68, it is necessary that the density of the flood beam 69 be greater than the density of the secondary emission from the surface of insulator screen 27 due to impingement of the higher current writing beam 68 thereon.

it will be observed that in the illustrated embodiment with the load resistor 64 and output circuits 65, 66 coupled to the metal backing screen 28 of the storage electrode 26, an output signal duplicative of the input video signal is provided, i.e., if the input video signal is white negative a white negative output signal will be developed across load resistor 64. It will be seen that the same current variation in reverse is provided in the circuit of the collector screen 29 during electrical read-out and thus the load resistor 64 of the output circuit 65, 66 may be coupled to the collector screen 29 to thereby provide a white positive output signal.

Referring now to FIG. 2 in which like elements are indicated by like reference numerals, in order to eliminate 60 and 120 cycle pick-up from the phosphor and collector voltages during electrical read-out, it may be desirable to pulse or chop the higher beam current writing beam at a high rate compared with the bandwidth of the video signal. Here, control grid 22 of the writing gun 17 is again coupled by capacitor 58 and switch element 54 in its first position 56 to video signal input terminal 59; however, switch element 54 in its second position 57, i.e., its electrical read-out position, couples conventional oscillator 67 to control grid 22 by means of capacitor 58. Switch element 55 in its first or normal writing and erasing position 56 again couples bias voltage source 61) to control grid 22, and in its second or electrical read-out position 57, couples bias voltage source 63 thereto to provide the higher beam current, as above described. A conventional diode clamp circuit 68 is desirably provided for coupling the bias voltage sources to the control grid 22.

In order to demodulate the electrical read-out signal to remove the oscillator frequency, backing screen 28 of the storage screen 26 is coupled to tank circuit 75 comprising inductance 70 and capacitor 71, tank circuit 75 being tuned to the frequency of oscillator 67 and thus presenting high impedance to the oscillator frequency and low impedance to all other frequencies. Tank circuit 75 is in turn coupled to switch 35 which in its position 36 is coupled to writing potential source 38 and in its position 37 it is coupled to erasing potential source 39. The electrical read-out signal is taken from tank circuit 75 by means of a conventional bandpass amplifier 72 coupled to inductance 70 by coupling capacitor 73 and a conventional video detector 74 coupling bandpass amplifier 72 to electrical read-out terminal 65. In this embodiment, it is desirable that the frequency of oscillator 67 be at least twice that of the bandpass frequency of the input video signal. It will be seen that the embodiment of FIG. 2 eliminates the necessity for employing the high resistance load resistor 64 in the backing screen circuit. As in the case of the embodiment of FIG. 1, tank circuit 75 and the electrical read-out circuit of FIG. 2 may alternatively be coupled in the circuit of collector screen 29.

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

An image storage tube selectively providing visual and electrical read-out comprising a phosphor display screen, a charge storage screen including an insulator screen and a metal backing screen, collector electrode means for collecting secondary electrons emitted by said insulator screen, a writing electron beam gun providing a writing beam, means applying a modulating signal to said writing beam, means for scanning the writing beam over said insulator screen to store said signal as a charge image thereon, a flood electron beam gun providing a flood beam, means selectively applying said flood beam to display said image on said phosphor screen and to erase said storage screen to the cut-off condition, and means for selectively increasing the beam current of said writing beam to the saturation level and scanning said insulator screen while simultaneously flooding said insulator screen with said flood beam; and output means detecting the current flow in said backing screen during said last named scanning to provide an output signal.

2. A system for selectively providing signal-to-image and signal -to-signal conversion comprising: a charge storage tube including display screen means, perforate charge storage electrode means comprising an insulator screen and a conductive screen; first means for forming and directing a high velocity writing electron beam toward said insulator screen and including means for scanning said writing beam over said insulator screen and means for intensity modulating said writing beam; second means for forming and directing a low velocity flood electron beam toward said insulator screen; collector electrode means for collecting secondary electrons emitted by said insulator screen due to impingement of said writing beam thereon; first switching means coupled to said first means for selectively initiating said writing beam; second switching means coupled to said second means for selectively initiating said flood beam; third switching means coupled to said modulating means and having first and second positions, said third switching means in said first position thereof coupling said modulating means to a source of video signals and to a first reference potential source for providin said writing beam with a first maximum beam current for storing an image on said insulator screen, said third switching means in said second position thereof decoupling said modulating means from said video signal source and said first reference potential source and coupling said modulating means to a second source of reference potential for providing said writing beam with a second maximum beam current higher than said first beam current; fourth switching means for selectively coupling said conductive screen to a source of writing potential and to a source of erasing potential, said flood beam selectively being modulated by said insulator screen to display said image on said display screen and erasing said insulator screen; and output circuit means coupled to one of said electrode means providing an output signal when said third switching means is in said second position and said second switching means simultaneously initiates said flood beam.

3. The system of claim 2 wherein said output circuit means is coupled to said conductive screen.

4. The system of claim 2 wherein each of said writing beam and flood beam forming means includes cathode means connected to respective sources of reference potential, wherein said erasing potential is positive with respect to said flood beam cathode means whe eby said flood beam charges said insulator screen to essentially the otential of said flood beam cathode means, wherein said writing potential is less positive than said erasing potential whereby the potential of said insulator screen is initially reduced below that of said flood beam cathode means, wherein said writing beam cathode means potential is negative with respect to said writing and erasing potentials and said first beam current causes selective charging of said insulator screen from said reduced potential level toward that of said flood beam cathode means by secondary emission, wherein said sec-0nd beam current tends to charge said insulator screen positive with respect to said 7 flood beam cathode means by secondary emission, and wherein said flood beam forming means provides a flood beam density greater than the density of the secondary emission from said insulator screen caused by said writing beam having said second beam current.

5. The system of claim 2 further comprising oscillator means, said third switching means in said second position thereof coupling said modulating means to said oscillator means.

6. The system or" claim 5 wherein said oscillator means has a frequency at least twice the pass band of said video signal source.

7. The system of claim 5 further comprising tuned circuit means coupled to said conductive screen and tuned to the frequency of said oscillator means, said output circuit means being coupled to said tuned circuit means and including video detecting means for removing the frequency of said oscillator means from the output signal therein.

References Cited UNITED STATES PATENTS 2,837,643 ii/1958 Goodwin et al 25027 3,853,702 19/1958 Johnson et al 343-7.7 2,953,711 9/1960 Taubenslag et a1 31512 3,002,124 19/1961 Schneeberger 315-12 3,214,516 .iO/ 1965 Anderson 1786.8 3,277,333 .lO/l966 Williams et a1 31512 ROBERT L. GRIFFIN, Primal-y Examiner.

JOHN W. CALDWELL, Examiner. 0 R. BLUM, issistarzt Examiner. 

